60
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What general tips can you give for golfing in Ruby?

I'm looking for ideas that can be applied to code golf problems in general that are specific to Ruby. (For example, "Remove comments" would not be an answer.)

Please post one tip per answer.

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  • \$\begingroup\$ Someone needs to write a language called Rub, which uses a single Unicode character for every Ruby token, kinda like Jelly and Pyth :) \$\endgroup\$ – Mark Thomas Aug 30 '17 at 12:28

48 Answers 48

42
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  • The numbers 100 to 126 can be written as ?d to ?~ in 1.8.
  • On a similar note if you need a single-character string in 1.9 ?x is shorter than "x".
  • If you need to print a string without appending a newline, $><<"string" is shorter than print"string".
  • If you need to read multiple lines of input $<.map{|l|...} is shorter than while l=gets;...;end. Also you can use $<.read to read it all at once.
  • If you're supposed to read from a file, $< and gets will read from a file instead of stdin if the filename is in ARGV. So the golfiest way to reimplement cat would be: $><<$<.read.
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  • \$\begingroup\$ ?x yields the ascii code in general, so you can realistically get all the printables to digits in two characters. 1.9 is different, 'a'.ord yields the ascii number, but is four bytes longer than the decimal version. \$\endgroup\$ – Hiato Feb 3 '11 at 8:03
  • 7
    \$\begingroup\$ An even golfier way to implement cat is to leave the ruby file completely empty (0 bytes) and insist that it should be run from the command line with the -p flag. \$\endgroup\$ – daniero Jul 17 '13 at 20:01
  • 1
    \$\begingroup\$ or, from @daniero's own answer, puts *$< \$\endgroup\$ – Not that Charles Jul 2 '14 at 19:15
  • 1
    \$\begingroup\$ So in 1.8, all I have to do is go ?~ and it will return 126? \$\endgroup\$ – Simply Beautiful Art May 13 '17 at 13:09
  • 3
    \$\begingroup\$ You can go beyond 126 using thinks like or , or if you are crazy enough: ?﷽.ord=65021 \$\endgroup\$ – Simply Beautiful Art May 13 '17 at 15:45
31
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Use the splat operator to get the tail and head of an array:

tail, *head = [1,2,3]
tail => 1
head => [2,3]

This also works the other way:

*head, tail = [1,2,3]
head => [1,2]
tail => 3

Use the * method with a string on an array to join elements:

[1,2,3]*?,
=> "1,2,3"
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26
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  • Use abort to terminate the program and print a string to STDERR - shorter than puts followed by exit
  • If you read a line with gets, you can then use ~/$/ to find its length (this doesn't count a trailing newline if it exists)
  • Use [] to check if a string contains another: 'foo'['f'] #=> 'f'
  • Use tr instead of gsub for character-wise substitutions: '01011'.tr('01','AB') #=> 'ABABB'
  • If you need to remove trailing newlines, use chop instead of chomp
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  • 2
    \$\begingroup\$ +1 for abort and ~/$/ \$\endgroup\$ – J-_-L Jun 26 '11 at 22:13
  • \$\begingroup\$ Please explain how to use ~/$/ \$\endgroup\$ – Mathieu CAROFF Nov 25 '18 at 6:47
  • \$\begingroup\$ @MathieuCAROFF every time you call gets, its result is stored in the $_ variable. /regex/ ~= string returns the index of the first match. Calling ~ on a regex is equivalent to /regex/ ~= $_. So it would be something like s=gets;l= ~/$/ \$\endgroup\$ – Cyoce Feb 8 at 3:18
18
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End your end.

Try to remove end from your code.

Don't use def...end to define functions. Make a lambda with the new -> operator in Ruby 1.9. (The -> operator is a "stabby lambda", or "dash rocket".) This saves 5 characters per function.

# 28 characters
def c n
/(\d)\1/=~n.to_s
end

# 23 characters, saves 5
c=->n{/(\d)\1/=~n.to_s}

Method calls are c n or c(n). Lambda calls are c[n]. Changing each c n to c[n] costs 1 character, so if you can use c n more than 5 times, then keep the method.

All methods that take do...end blocks can take {...} blocks instead. This saves 3 to 5 characters. If the precedence of {...} is too high, then use parentheses to fix it.

# 48 characters
(?a..?m).zip (1..5).cycle do|a|puts a.join','end

# WRONG: passes block to cycle, not zip
(?a..?m).zip (1..5).cycle{|a|puts a.join','}

# 45 characters, saves 3
(?a..?m).zip((1..5).cycle){|a|puts a.join','}

Replace if...else...end with the ternary operator ?:. If a branch has two or more statements, wrap them in parentheses.

# 67 characters
if a<b
puts'statement 1'
puts'statement 2'else
puts'statement 3'end

# 62 characters, saves 5
a<b ?(puts'statement 1'
puts'statement 2'):(puts'statement 3')

You probably don't have while or until loops, but if you do, then write them in modifier form.

(a+=1
b-=1)while a<b
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  • \$\begingroup\$ Are the parentheses around puts'statement 3' necessary? \$\endgroup\$ – Cyoce Dec 2 '16 at 2:38
15
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Addition to w0lf

When working with arrays, .compact can be replaced with -[nil] to save 2 chars.

Combined with above -> you can make it even shorter with -[p] to save another 2 chars.

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14
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Use the short predefined variables wherever possible, e.g. $* instead of ARGV. There's a good list of them here, along with a lot of other useful information.

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11
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If you need to find if a particular element e is inside a range r, you can use

r===e

instead of the longer:

r.cover?(e) # only works if `r.exclude_end?` is false

or

r.member?(e)

or

r.include?(e)
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  • 3
    \$\begingroup\$ Isn’t r===e even shorter? \$\endgroup\$ – akuhn Jun 1 '12 at 21:10
  • \$\begingroup\$ @akuhn Yes, it is. Much Shorter. Thanks for pointing that out, it helped me shorten my code by 10 chars, which is huge: codegolf.stackexchange.com/a/6125/3527 \$\endgroup\$ – Cristian Lupascu Jun 1 '12 at 21:20
  • 1
    \$\begingroup\$ You’re welcome. Everything that can be used in a switch statement has === implemented. \$\endgroup\$ – akuhn Jun 2 '12 at 12:49
11
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When you are using string interpolation, (as you should pr Martin Büttner's post), you don't need the curly brackets if your object has a sigil ($, @) in front of it. Useful for magical variables like $_, $&, $1 etc:

puts "this program has read #$. lines of input"

So also if you need to print a variable more than you use it otherwise, you may save some bytes.

a=42; puts "here is a: #{a}"; puts "here is a again: #{a}"
$b=43; puts "here is b: #$b"; puts "here is b again: #$b"
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10
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$_ is last read line.

  • print - if no argument given print content of $_
  • ~/regexp/ - short for $_=~/regexp/

In Ruby 1.8, you have four methods in Kernel that operate on $_:

  • chop
  • chomp
  • sub
  • gsub

In Ruby 1.9, these four methods exist only if your script uses -n or -p.

If you want to print some variable often then use trace_var(:var_name){|a|p a}

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  • 2
    \$\begingroup\$ These are only available when you run Ruby with the -p or -n option. Reference. \$\endgroup\$ – Darren Stone Dec 27 '13 at 19:12
  • 1
    \$\begingroup\$ It seems that trace_var only works with global $variables \$\endgroup\$ – daniero Mar 23 '16 at 8:56
10
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Avoid length in if a.length<n

length is 6 bytes, a bit costly in code golf. in many situations, you can instead check if the array has anything at a given point. if you grab past the last index you will get nil, a falsey value.

So you can Change:

if a.length<5 to if !a[4] for -5 bytes

or

if a.length>5 to if a[5] for -6 bytes

or

if a.length<n to if !a[n-1] for -3 bytes

or

if a.length>n to if a[n] for -6 bytes

Note: will only work with an array of all truthy values. having nil or false within the array may cause problems.

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  • 4
    \$\begingroup\$ I always use size… But this is definitely better. BTW, works for String too. \$\endgroup\$ – manatwork Dec 7 '15 at 17:06
9
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Use string interpolation!

  1. To replace to_s. If you need parentheses around whatever you want to turn into a string, to_s is two bytes longer than string interpolation:

    (n+10**i).to_s
    "#{n+10**i}"
    
  2. To replace concatenation. If you concatenate something surrounded by two other strings, interpolation can save you one byte:

    "foo"+c+"bar"
    "foo#{c}bar"
    

    Also works if the middle thing is itself concatenated, if you just move the concatenation inside the interpolation (instead of using multiple interpolations):

    "foo"+c+d+e+"bar"
    "foo#{c+d+e}bar"
    
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9
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If you ever need to get a number from ARGV, get, or something similar to do something that many times, instead of calling to_i on it, you can just use ?1.upto x{do something x times} where x is a string.

So using ?1.upto(a){} instead of x.to_i.times{} will save you 2 characters.

You can also re-write things like p 1 while 1 or p 1 if 1 as p 1while 1 or p 1if 1

That example isn't very useful, but it could be used for other things.

Also, if you need to assign the first element of an array to a variable, a,=c will save two characters as opposed to a=c[0]

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9
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Don't use the true and false keywords.

Use:

  • !p for true (thanks, histocrat!)
  • !0 for false. If all you need is a falsy value, then you can simply use p (which returns nil).

to save some chars.

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  • 1
    \$\begingroup\$ Unless you actually need true (i.e. if a truthy value is enough, like in an if condition), you don't even need !!. \$\endgroup\$ – Martin Ender Aug 6 '14 at 6:31
  • 4
    \$\begingroup\$ And similarly, p (which evaluates to nil) is a shorter falsey value. Which means the shortest way to get true is !p. \$\endgroup\$ – histocrat Aug 6 '14 at 22:17
  • \$\begingroup\$ @histocrat good point! I've edited my answer. \$\endgroup\$ – Cristian Lupascu Aug 7 '14 at 6:26
8
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Build arrays using a=i,*a to get them in reverse order. You don't even need to initialize a, and if you do it doesn't have to be an array.

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8
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New features in Ruby 2.3 and 2.4

It's good to stay abreast of new language features that will help your golf game. There are a few great ones in the latest Rubies.

Ruby 2.3

The safe navigation operator: &.

When you call a method that might return nil but you want to chain additional method calls if it's not, you waste bytes handling the nil case:

arr = ["zero", "one", "two"]
x = arr[5].size
# => NoMethodError: undefined method `size' for nil:NilClass

x = arr[5].size rescue 0
# => 0

The "safe navigation operator" stops the chain of method calls if one returns nil and returns nil for the whole expression:

x = arr[5]&.size || 0
# => 0

Ruby 2.4

Ruby 2.4 isn't out yet, but it will be soon and has some great little features. (When it's released I'll update this post with some links to the docs.) I learned about most of these in this great blog post.

Enumerable#sum

No more arr.reduce(:+). You can now just do arr.sum. It takes an optional initial value argument, which defaults to 0 for Numeric elements ([].sum == 0). For other types you'll need to provide an initial value. It also accepts a block that will be applied to each element before addition:

[[1, 10], [2, 20], [3, 30]].sum {|a,b| a + b }
# => 66

Integer#digits

This returns an array of a number's digits in least-to-greatest significance order:

123.digits # => [3, 2, 1]

Compared to, say, 123.to_s.chars.map(&:to_i).reverse, this is pretty nice.

As a bonus, it takes an optional radix argument:

a = 0x7b.digits(16) => [11, 7]
a.map{|d|"%x"%d} => ["b", "7"]

Precision argument for Numeric#ceil, floor, and truncate:

Math::E.ceil(1) # => 2.8
Math::E.floor(1) # => 2.7
(-Math::E).truncate(1) # => -2.7

Multiple assignment in conditionals

This raises an error in earlier versions of Ruby, but is allowed in 2.4.

(a,b=1,2) ? "yes" : "no" # => "yes"
(a,b=nil) ? "yes" : "no" # => "no"
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  • \$\begingroup\$ Golf Math::E.ceil(1) to Math::E.ceil 1, and likewise for floor and truncate. \$\endgroup\$ – Simply Beautiful Art Nov 20 '17 at 23:38
  • 1
    \$\begingroup\$ @SimplyBeautifulArt I expect that someone golfing in Ruby will be able to make that leap themselves. \$\endgroup\$ – Jordan Nov 20 '17 at 23:50
  • \$\begingroup\$ For Enumerable#sum, .flatten.sum is 2 bytes shorter than .sum{|a,b|a+b} \$\endgroup\$ – Asone Tuhid Jan 24 '18 at 10:45
  • \$\begingroup\$ (-Math::E).truncate(1) is equivalent to -Math::E.truncate(1) which is 1 byte shorter \$\endgroup\$ – Asone Tuhid Mar 1 '18 at 12:21
  • 1
    \$\begingroup\$ &. can be used with subscripting like this a&.[]i (1 byte shorter than a&.at i). Although, if brackets are required, a||a[i] is 1 byte is shorter than a&.[](i) or a&.at(i) \$\endgroup\$ – Asone Tuhid Mar 1 '18 at 12:24
7
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Scientific notation can often be used to shave off a char or two:

x=1000
#versus
x=1e3
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  • 9
    \$\begingroup\$ Note: This will return a Float value (1000.0) instead of an Integer, which may cause inaccurate results with large numbers. \$\endgroup\$ – Dogbert Feb 25 '11 at 11:02
  • 4
    \$\begingroup\$ Ah, nice 1e2 is better than 100.0 when a percentage is needed. \$\endgroup\$ – Phrogz Feb 26 '11 at 6:36
  • \$\begingroup\$ Similar to this principle, 1.0* is 1 char shorter than .to_f \$\endgroup\$ – Unihedron Dec 16 '17 at 13:44
7
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Use operator methods instead of parentheses

Let's say you want to express a*(b+c). Because of precedence, a*b+c won't work (obviously). Ruby's cool way of having operators as methods comes to the rescue! You can use a.*b+c to make the precedence of * lower than that of +.

a*(b+c) # too long
a*b+c   # wrong
a.*b+c  # 1 byte saved!

This can also work with the ! and ~ operators (things like unary + or unary - don't work because their methods are -@ and +@, saving () but adding .@)

(~x).to_s # too long
~x.to_s   # error
x.~.to_s  # 1 byte saved!
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6
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Use || instead or and && instead and.

Beside the one character from and you can save the spaces (and perhaps the bracket) around the operator.

p true and false ? 'yes' :'no'   #-> true (wrong result)
p (true and false) ? 'yes' :'no' #-> 'no'
p true&&false ? 'yes' :'no'      #-> 'no', saved 5 characters


p true or false ? 'yes' :'no'   #-> true (wrong result)
p (true or false) ? 'yes' :'no' #-> 'yes'
p true||false ? 'yes' :'no'      #-> 'yes', saved 4 characters

If you loop on an array you normally use each. But map loops also over an array and it is one character shorter.

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6
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I just attempted a TDD code-golf challenge i.e. Write shortest code to make specs pass. The specs were something like

describe PigLatin do
  describe '.translate' do
    it 'translates "cat" to "atcay"' do
      expect(PigLatin.translate('cat')).to eq('atcay')
    end
    # And similar examples for .translate
  end
end

For the sake of code-golf, one need not create a module or class.

Instead of

module PigLatin def self.translate s;'some code'end;end

one can do

def(PigLatin=p).translate s;'some code'end

Saves 13 characters!

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  • 7
    \$\begingroup\$ Ha, very thorough. Not only did you add the necessary behavior to PigLatin, but also to @pig_latin, $pig_latin, and 'pig'['latin']. \$\endgroup\$ – histocrat Feb 27 '14 at 15:23
  • \$\begingroup\$ @histocrat: Now I get it. It's because translate has been defined on nil. \$\endgroup\$ – Eric Duminil Mar 20 '17 at 13:48
6
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Kernel#p is a fun method.

Use p var instead of puts var. This works perfectly with integers and floats, but not with all types. It prints quotation marks around strings, which is probably not what you want.

Used with a single argument, p returns the argument after printing it.

Used with multiple arguments, p returns the arguments in an array.

Use p (with no arguments) instead of nil.

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  • 10
    \$\begingroup\$ Unfortunately p 'some string' prints "some string" and not just some string which is often criticised by others. \$\endgroup\$ – Patrick Oscity Jun 1 '13 at 21:11
  • 1
    \$\begingroup\$ Basically p s is the same as puts s.inspect, but it returns s \$\endgroup\$ – Cyoce Nov 3 '16 at 23:37
6
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Don't use #each. You can loop over all elements just fine with #map. So instead of

ARGV.each{|x|puts x}

you can do the same in less bytes.

ARGV.map{|x|puts x}

Of course, in this case puts $* would be even shorter.


There are literals for rational and complex numbers:

puts 3/11r == Rational(3,11)
puts 3.3r == Rational(66,20)
puts 1-1.i == Complex(1,-1)

=> true
true
true

You can use most bytes within strings. "\x01" (6 bytes) can be shortened to "" (3 bytes). If you only need this one byte, this can be shortened even further to ? (2 bytes).

By the same token, you can get newlines shorter like this:

(0..10).to_a.join'
'

 => "0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10"

You can use ?\n and ?\t as well, which is one byte shorter than "\n" and "\t". For obfuscation, there also ?\s, a space.


Use constants instead of passing arguments around, even if you need to change them. The interpreter will give warnings to stderr, but who cares. If you need to define more variables related to each other, you can chain them like this:

A=C+B=7+C=9

=> A=17, B=16, C=9

This is shorter than C=9;B=16;A=17 or C=0;B=C+7;A=C+B.


If you need an infinite loop, use loop{...}. Loops of unknown length may be shorter with other loops:

loop{break if'
'==f(gets)}

while'
'!=f(gets);end

Some more gsub/regexp tricks. Use the special '\1' escape characters instead of a block:

"golf=great short=awesome".gsub(/(\w+)=(\w+)/,'(\1~>\2)')

"golf=great short=awesome".gsub(/(\w+)=(\w+)/){"(#{$1}~>#{$2})")

And the special variables $1 etc. if you need to perform operations. Keep in mind they are defined not only inside the block:

"A code-golf challenge." =~ /(\w+)-(\w+)/
p [$1,$2,$`,$']

=> ["code", "golf", "A ", " challenge."] 

Get rid of spaces, newlines, and parentheses. You can omit quite a bit in ruby. If in doubt, always try if it works without, and keep in mind this might break some editor syntax highlighting...

x+=1if$*<<A==????::??==??
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  • \$\begingroup\$ "Please post one tip per answer." Also ?\n is nice, but not really shorter than actually putting a newline character inside quotes. (same for tab) \$\endgroup\$ – Martin Ender May 7 '15 at 23:29
  • \$\begingroup\$ And puts$* is even shorter. \$\endgroup\$ – Cyoce Nov 7 '17 at 5:20
  • \$\begingroup\$ I know you were trying to prove a point but I'm pretty sure that last example is the same as x+=1;$*<<A \$\endgroup\$ – Asone Tuhid Mar 1 '18 at 14:03
6
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Yet another way to use the splat operator: if you want to assign a single array literal, a * on the left-hand side is shorter than brackets on the right-hand side:

a=[0]
*a=0

With multiple values you don't even need the splat operator (thanks to histocrat for correcting me on that):

a=[1,2]
a=1,2
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  • \$\begingroup\$ The latter case doesn't actually need the splat. \$\endgroup\$ – histocrat Aug 15 '15 at 22:53
  • \$\begingroup\$ @histocrat Oh wow, I thought the second value would just be discarded in that case. \$\endgroup\$ – Martin Ender Aug 15 '15 at 22:53
  • 1
    \$\begingroup\$ I can't believe I haven't known these in all the time I've spent golfing in Ruby. \$\endgroup\$ – Doorknob Jan 2 '16 at 3:07
6
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When a challenge requires that you output multiple lines, you don't have to loop through your results in order to print each line of e.g. an array. The puts method will flatten an array and print each element on a separate line.

> a = %w(testing one two three)
> puts a
testing
one
two
three

Combining the splat operator with #p you can make it even shorter:

p *a

The splat operator (technically the *@ method, I think) also casts your non-array enumerables to arrays:

> p a.lazy.map{|x|x*2}
#<Enumerator::Lazy: #<Enumerator::Lazy: [1, 2, 3]>:map>

vs

> p *a.lazy.map{|x|x*2}
2
4
6
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  • 1
    \$\begingroup\$ *@ is not a method, splat is syntactic sugar \$\endgroup\$ – Asone Tuhid Jan 24 '18 at 10:55
6
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Save some bytes when removing repeated elements of an array

a.uniq # before
a|[]   # after
    ^^

If you will be using an empty array [] in a variable, you can save even more bytes:

a.uniq;b=[] # before
a|b=[]      # after
      ^^^^^
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  • 1
    \$\begingroup\$ For the first case, a&a is 1 byte shorter \$\endgroup\$ – Asone Tuhid Mar 7 '18 at 12:59
5
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Use Goruby instead of Ruby, which is something like an abbreviated version of Ruby. You can install it with rvm via

rvm install goruby

Goruby allows you to write most of your code as you would be writing Ruby, but has additional abbreviations built in. To find out the shortest available abbreviation for something, you can use the helper method shortest_abbreviation, for example:

shortest_abbreviation :puts
#=> "pts"

Array.new.shortest_abbreviation :map
#=> "m"

String.new.shortest_abbreviation :capitalize
#=> "cp"

Array.new.shortest_abbreviation :join
#=> "j"

Also very handy is the alias say for puts which itself can be abbreviated with s. So instead of

puts [*?a..?z].map(&:capitalize).join

you can now write

s [*?a..?z].m(&:cp).j

to print the alphabet in capitals (which is not avery good example). This blog post explains more stuff and some of the inner workings if you are interested in further reading.

PS: don't miss out on the h method ;-)

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5
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To join an array, instead of this

[...].join

do this

[...]*''

which saves 2 bytes. To join with a separator use

[...]*?,
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5
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Subscripting Numbers!

I just discovered this yesterday. n[i] returns n's bit at the i-th position. Example:

irb(main):001:0> n = 0b11010010
=> 210
irb(main):002:0> n[0]
=> 0
irb(main):003:0> n[1]
=> 1
irb(main):004:0> n[2]
=> 0
irb(main):005:0> n[3]
=> 0
irb(main):006:0> n[4]
=> 1
irb(main):007:0> n[5]
=> 0
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4
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You may be able to save 2 chars and use

[*(...)]

instead of

(...).to_a

For example, suppose we have a range that we want as an array:

(1..2000).to_a

Just do it like this:

[*1..2000]  #  Parentheses around the (ran..ge) is not needed!

And now you have your range as an array.

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  • 5
    \$\begingroup\$ I think [*1..2000] works, too? \$\endgroup\$ – Lynn Aug 24 '15 at 18:38
4
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Array#assoc/rassoc

When you have an array of arrays and want to find the sub-array that starts with a particular value, don't use Enumerable#find, use Array#assoc:

a = [[0,"foo"],[0,"bar"],[1,"baz"],[0,"qux"]]
a.find{|x,|x==1} # => [1,"baz"]
a.assoc(1) # => [1,"baz"]

This is also a good replacement for Enumerable#any? in some situations.

Array#rassoc does the same thing, but checks the sub-arrays' last element:

a = [[123,"good"],[456,"good"]]
a.any?{|*,x|x=="bad"} # => false
a.rassoc("bad") # => nil
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  • \$\begingroup\$ For the a.any? line in the rassoc example, what does |x,| do? How is it different from |x|? \$\endgroup\$ – Cyoce Nov 4 '16 at 1:05
  • \$\begingroup\$ @Cyoce Block parameter destructuring follows the same rules as destructuring assignment, so it's like x=[1,2] vs x,=[1,2]. Using my example above, with |x|, in the first iteration x will be [0,"foo"]. With |x,y|, x will be 0 and y will be "foo". Likewise, with |x,|, x will be 0. In other words, it says "put the first element in x and throw the rest away. \$\endgroup\$ – Jordan Nov 4 '16 at 1:27
  • \$\begingroup\$ Note that it doesn't work in reverse, e.g. |,y| is a SyntaxError, ergo |_,y|. But I've just now realized that |*,y| works, which is cleaner than using a variable named _ (but no shorter). \$\endgroup\$ – Jordan Nov 4 '16 at 1:39
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On looping

while...end

If you need to break out of the loop, while condition;code;end will probably be shorter than loop{code;condition||break}.

The ; before end is not always required, eg. while condition;p("text")end

until c;...;end is equivalent to while !c;...;end and 1 byte shorter.

Note that in most cases code while condition and code until condition are significantly shorter as they don't require the end keyword and can often drop semicolons. Also, i+=1 while true is equivalent to i+=1while true and 1 byte shorter.

redo

When run, the redo command jumps back to the beginning of the block it's in.

When using redo in a lambda, you will have to move any setup variables to the arguments to avoid them being reset at every iteration (see examples).

recursion

Recursion can be shorter is some cases. For instance, if you're working on an array element by element, something like f=->s,*t{p s;t[0]&&f[*t]} can be shorter than the alternatives depending on the stuff.

Note that per the current consensus, if you're calling your function by name, you need to include the assignment (f=) in the byte count making all recursive lambdas 2 bytes longer by default.

eval

If you need to run some code n times, you can use eval"code;"*n.

This will concatenate code; n times and run the whole thing.

Note that in most cases you need to include a ; after your code.

Examples

A lambda to print all numbers from 1 to a inclusive:

->n{i=0;loop{p i+=1;i<n||break}} # 32 bytes
f=->n,i=1{i>n||p(i)&&f[n,i+1]}   # 30 bytes
->n,i=0{p(i+=1)<n&&redo}         # 24 bytes
->n{i=0;p i+=1while i<n}         # 24 bytes
->n{i=0;eval"p i+=1;"*n}         # 24 bytes
->n{n.times{|i|p i+1}}           # 22 bytes # thanks to @benj2240

In this case, since the end-point is defined (n), the n.times loop is the shortest.

The redo loop works because i+=1 modifies i and returns its new value and p(x) returns x (this is not true of print and puts).

Given a function g and a number n, find the first number strictly larger than n for which g[n] is truthy

->g,n{(n+1..1/0.0).find{|i|g[i]}} # 33 bytes
->g,n{loop{g[n+=1]&&break};n}     # 29 bytes
f=->g,n{n+=1;g[n]?n:f[g,n]}       # 27 bytes
->g,n{1until g[n+=1];n}           # 23 bytes
->g,n{g[n+=1]?n:redo}             # 21 bytes

In this case, with an unknown end-point, redo is the best option.

The (n+1..Inf) loop is equivalent to simply looping indefinitely but more verbose.

A 1 (or anything else) is required before the until keyword to complete the syntax, using a number allows you to drop a space.

The eval method is not viable in this case because there is neither a defined end-point nor an upper bound.

\$\endgroup\$
  • 1
    \$\begingroup\$ .times can often be even shorter for fixed loops, eg ->n{n.times{|i|p i+1}} for 22 bytes \$\endgroup\$ – benj2240 Mar 16 '18 at 15:07

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